Firearms

Handguns

Nambu Type 14

Kitsurubami ceases fire as she realized that an 8mm pistol isn't doing much against the 200 foot tall robot.

A defeated Kitsurubami finally loses her temper.

Kitsurubami unloads her Nambu's at Kanti at point-blank range.

Beretta 92FS

In episode 5, a billboard hit by a stay shot during Haruhana's battle with the giant robot depicts a man holding a Beretta 92FS pistol. This is one of several references to John Woo's films throughout the OVA.

M16A1

Other

Rickenbacker 4001

Haruhara's Rickenbacker 4001 bass guitar is seen being used as something other than a musical instrument on several occasions, including an automatic shotgun (with a rifled barrel) during the gunfight during episode 5.

Haruhara reveals her guitar's shotgun feature.

Haruhara readies herself to ambush two IIB agents.

Haruhara guts an IIB agent with her guitar.

Misc. Weapons

Several of the agents from the Interstellar Immigration Bureau use weapons that are never seen clearly enough to positively identify or are drawn in a generic style.

Amarao backed by a roomful of IIB agents.

Three of the IIB agents walk into Haruhara's ambush.

Airsoft Guns

A large portion of episode 5, Brittle Bullet, centers around an airsoft game between several of the series protagonists. Given FLCL's tendency towards exaggeration, these replicas are shown ejecting brass and having muzzle flashes with each shot.

MAC-11

Naota Nandaba uses a pair of MAC-11 submachine guns during the airsoft game.

RPB Industries M11A1 - .380 ACP

Naota with his MAC-11s.

"Snipers are so annoying."

Uzi

Haruko Haruhara's airsoft gun of choice is an Uzi with a wood stock and handguard.

IMI Uzi with detachable wooden buttstock - 9x19mm

Haruhara fire's her Uzi at Kamon. Note the brass and muzzleflash.

"Not in a hundred thousand years will you ever get anything from me but a butt full of lead, compadre!"

Haruhara unloads her Uzi at Naota.

Franchi SPAS-12

During the airsoft game, Kanti uses a Franchi SPAS-12 shotgun with the stock removed. In addition to being portrayed as if it were a live-fire weapon, it is seen being fired on full auto (while the real SPAS-12 can only fire either pump-action or semi-auto).

Franchi SPAS-12 combat shotgun with no stock – 12 Gauge

Kanti with his SPAS-12.

"I'm leaving the rest to you, TV boy!"

Luger P08 "Artillery" Model

Kamon Nandaba's preferred airsoft weapon is a pair of Luger P08 "Artillery" Model pistols. He also has shoulder stocks attached to them in several scenes.

Luger P08 - 9x19mm. This is the long barreled "Artillery" model of the Luger P08 - 9x19mm

Kamon draws his P08, posing in a Lupin III reference.

Subtlety is not FLCL's strong suite.

Kamon Nandaba charges Naota, dual-wielding his P08's.

Over-sized Weapons

The giant robot in episode 5 is seen using several gargantuan firearms. As opposed to most mecha in anime that use specialized weaponry, this one uses weapons that are simply regular firearms that are scaled up to match its size.

On a side note, the battle between Haruhara and the robot (especially Harhara's bunny-girl outfit) is a self-referencing parody of the Daicon III and Daicon IV shortfilms that marked the animation debut of Studio Gainax's founders.